US20190163085A1 - Controller for Process Unit of Image Forming Apparatus, Method of Controlling the Same, and Non-Transitory Computer-Readable Storage Medium - Google Patents
Controller for Process Unit of Image Forming Apparatus, Method of Controlling the Same, and Non-Transitory Computer-Readable Storage Medium Download PDFInfo
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- US20190163085A1 US20190163085A1 US16/137,674 US201816137674A US2019163085A1 US 20190163085 A1 US20190163085 A1 US 20190163085A1 US 201816137674 A US201816137674 A US 201816137674A US 2019163085 A1 US2019163085 A1 US 2019163085A1
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- 230000008569 process Effects 0.000 title claims description 8
- 238000012546 transfer Methods 0.000 claims abstract description 107
- 238000012360 testing method Methods 0.000 claims description 23
- 238000012544 monitoring process Methods 0.000 claims 6
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- 238000012545 processing Methods 0.000 description 20
- 230000004044 response Effects 0.000 description 19
- 238000001514 detection method Methods 0.000 description 17
- 230000008859 change Effects 0.000 description 10
- 238000012937 correction Methods 0.000 description 6
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- 238000002474 experimental method Methods 0.000 description 4
- 238000004088 simulation Methods 0.000 description 4
- 230000001276 controlling effect Effects 0.000 description 3
- 238000009825 accumulation Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
- G03G15/0266—Arrangements for controlling the amount of charge
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
- G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
- G03G15/1665—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat
Definitions
- aspects disclosed herein relate to an image forming apparatus including a photosensitive member, a method of controlling the image forming apparatus, and a non-transitory computer-readable storage medium storing a program.
- Some known electrophotographic image forming apparatuses form a developer image onto a photosensitive layer of a photosensitive member.
- the photosensitive member contacts a member, and slides relative to the member during rotation. Sliding of the photosensitive member relative to the member causes friction therebetween, thereby causing charge accumulation inside the photosensitive layer of the photosensitive drum.
- Such charge accumulation may change a relationship between a charge current, which passes through a charger for charging the photosensitive member, and a surface potential of the photosensitive member, thereby failing to control the surface potential of the photosensitive drum to have a desired surface potential.
- an accumulated charge quantity in the photosensitive layer is predicted. Based on the prediction, the larger the accumulated charge quantity is present, the greater the absolute value is specified for a charge voltage or the charge current (e.g., the magnitude of the charge voltage or charge current is increased over the magnitude of an initial charge voltage or charge current). More specifically, in the known technique, the accumulated charge quantity is predicted based on, for example, a transfer current, a rotating speed of the photosensitive member, and/or temperature.
- Apparatus, methods, and computer-readable mediums are described for adjusting a charge voltage for a photosensitive member to account for accumulated charge quantity.
- currents related to charging a charger which imparts a charge to a photosensitive member, are monitored. Based on the monitored currents, a new charging voltage may be determined and applied that accounts for accumulated charge quantity in the photosensitive member.
- a transfer current related to a transfer charge may also be monitored or a predetermined value used. The determination of the new charging voltage may be performed at various times.
- FIG. 1 is a sectional view illustrating an image forming apparatus in a first illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 2 illustrates an internal configuration of the image forming apparatus in the first illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 3 is a diagram for explaining how to calculate a charge quantity in a circumferential surface of a photosensitive drum in the first illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 4 is a flowchart of processing executed by a controller in the first illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 5 is a flowchart of current I EX1 calculation in the first illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 6 is a flowchart of processing executed by the controller in a second illustrative embodiment according to one or more aspects of the disclosure.
- FIG. 7 is a graph showing a relationship between a charge voltage, a current I EX , and an accumulated charge quantity in the second illustrative embodiment according to one or more aspects of the disclosure.
- the image forming apparatus may be a laser printer 1 .
- the laser printer 1 is configured to form an image onto a sheet S (an example of a transfer medium).
- the laser printer 1 includes a casing 2 , a feed tray 3 , a multipurpose tray 4 , a process unit 5 , a fixing unit 6 , and a controller 100 .
- the laser printer 1 further includes a display 35 .
- the process unit 5 is configured to form a developer image onto a sheet S.
- the process unit 5 includes a photosensitive drum 7 (an example of a photosensitive member), a charge roller 8 (an example of a charger), a transfer roller 9 (an example of a transfer member), a scanner 10 , and a developer cartridge 20 .
- the scanner 10 is disposed in an upper portion of the casing 2 .
- the scanner 10 includes a laser source (not illustrated), a polygon mirror 11 , reflectors 12 and lenses (not illustrated).
- the laser source emits a laser beam.
- the emitted laser beam travels to a circumferential surface of the photosensitive drum 7 while being reflected off the polygon mirror 11 and the reflectors and passing through the lenses.
- the laser beam scans the circumferential surface of the photosensitive drum 7 at a high scanning speed.
- the developer cartridge 20 includes a housing 21 , an agitator 25 , a developing roller 27 , a supply roller 28 , and a blade 29 for regulating a thickness of a toner layer.
- the housing 21 is configured to store toner T (an example of developer) therein.
- the housing 21 supports the agitator 25 , the developing roller 27 , and the supply roller 28 rotatably.
- the charge roller 27 faces the photosensitive drum 7 .
- the supply roller 28 supplies toner T from a developer chamber of the housing 21 onto a circumferential surface of the developing roller 27 .
- the developing roller 27 further supplies toner T onto the circumferential surface of the photosensitive drum 7 .
- the photosensitive drum 7 includes a cylindrical base, and a photosensitive layer formed on an outer circumferential surface of the cylindrical base.
- the cylindrical base may be made of, for example, metal.
- the photosensitive drum 7 is configured to rotate clockwise in FIG. 1 .
- the photosensitive layer may be positively chargeable.
- the photosensitive layer may include a single layer.
- the photosensitive layer may be applied with coating for protection and/or increase of durability.
- the charge roller 8 is disposed above the photosensitive drum 7 .
- the charge roller 8 is configured to rotate while being in contact with the circumferential surface, i.e., the photosensitive layer, of the photosensitive drum 7 .
- the transfer roller 9 faces the photosensitive drum 7 .
- the transfer roller 9 is disposed below the photosensitive drum 7 .
- the laser printer 1 further includes a cleaning blade 15 .
- the cleaning blade 15 is disposed downstream from the transfer roller 9 in a rotating direction of the photosensitive drum 7 .
- the cleaning blade 15 has one end that is in contact with the circumferential surface, i.e., the photosensitive layer, of the photosensitive drum 7 .
- the laser printer 1 further includes an LED lamp 16 .
- the LED lamp 16 is disposed downstream from the cleaning blade 15 in the rotating direction of the photosensitive drum 7 .
- the photosensitive drum 7 may be positively charged by the charge roller 8 during rotation.
- the scanner 10 then exposes the circumferential surface of the photosensitive drum 7 with a laser beam to form an electrostatic latent image thereon.
- the developing roller 27 supplies toner T onto the circumferential surface of the photosensitive drum 7 to form a toner image on the circumferential surface of the photosensitive drum 7 .
- a sheet S passes between the photosensitive drum 7 and the transfer roller 9
- the toner image is transferred onto the sheet P from the photosensitive drum 7 by application of a transfer bias to the transfer roller 9 .
- the fixing unit 6 is disposed downstream from the process unit 5 in a direction in which a sheet S is conveyed.
- the fixing unit 6 includes a fixing roller 6 A and a pressure roller 6 B.
- the pressure roller 6 B presses the fixing roller 6 A.
- the fixing roller 6 A includes a cylindrical body and a heater in an internal space of the cylindrical body. The fixing unit 6 fixes the toner image onto the sheet S by heat applied by the heater while sandwiching the sheet S between the fixing roller 6 A and the pressure roller 6 B.
- the controller 100 is configured to execute various operation controls such as receipt of print data, sheet feeding from the feed tray 3 or the multipurpose tray 4 , operations of various units such as the process unit 5 and the fixing unit 6 , in accordance with one or more preinstalled programs.
- the one or more programs enable the controller 100 to execute various processing as described below.
- the controller 100 includes a single or a plurality of electric circuits such as a CPU 110 , a ROM 120 , and a RAM 130 .
- the ROM 120 stores programs for controlling units and members of the laser printer 1 and various data such as various settings.
- the RAM 130 is used by the CPU 110 as a work space for executing the programs and as a storage space for storing data temporarily.
- the CPU 110 executes various calculations based on, for example, instructions outputted by an external device (not illustrated) such as a general-purpose computer, signals outputted by a current sensor 31 A (an example of a first sensor) or by a current sensor 32 A (an example of a second sensor), the one or more programs and/or data read from the ROM 120 .
- the controller 100 is configured to control the units and members of the laser printer 1 by outputting control signals to those units and members based on calculation results of the CPU 110 .
- the controller 100 is further configured to output, to the external device (e.g., the computer), signals responsive to an operating status of the laser printer 1 .
- the controller 100 is configured to control operations of the photosensitive drum 7 , the charge roller 8 , the transfer roller 9 , the developing roller 27 , the LED lamp 16 , and the scanner 10 .
- the laser printer 1 further includes a motor 17 and a plurality of gears (not illustrated).
- the motor 17 is connected to the photosensitive drum 7 via the plurality of gears.
- the motor 17 is configured to drive the photosensitive drum 7 .
- the controller 100 is configured to control motion of the photosensitive drum 7 by outputting a control signal such as a pulse width modulation (“PWM”) signal to the motor 17 . More specifically, for example, the controller 100 controls the photosensitive drum 7 to start or stop rotating via the motor 17 .
- PWM pulse width modulation
- the charge roller 8 is electrically connected to a charge voltage application circuit 31 .
- the charge voltage application circuit 31 is further electrically connected to the controller 100 .
- the charge voltage application circuit 31 is configured to apply a charge voltage to the charge roller 8 .
- the controller 100 is further configured to control the charge voltage application circuit 31 by outputting a control signal such as a PWM signal to the charge voltage application circuit 31 . More specifically, for example, the controller 100 controls the charge voltage application circuit 31 to supply electric power to the charge roller 8 .
- the controller 100 specifies a charge voltage to be applied to the charge roller 8 such that the surface potential of the circumferential surface of the photosensitive drum 7 becomes a predetermined potential.
- the charge voltage application circuit 31 is connected to the current sensor 31 A.
- the current sensor 31 A is configured to detect a charge current passing through the charge roller 8 .
- the current sensor 31 A is further configured to output, to the controller 100 , a detection signal corresponding to a charge current passing through the charge roller 8 when the charge voltage application circuit 31 applies a charge voltage to the charge roller 8 .
- the transfer roller 9 is electrically connected to a transfer voltage application circuit 32 .
- the transfer voltage application circuit 32 is further electrically connected to the controller 100 .
- the transfer voltage application circuit 32 is configured to apply a transfer voltage to the transfer roller 9 .
- the controller 100 is further configured to control the transfer voltage application circuit 32 by outputting a control signal such as a PWM signal to the transfer voltage application circuit 32 . More specifically, for example, the controller 100 controls the transfer voltage application circuit 32 to supply electric power to the transfer roller 9 .
- the controller 100 controls a transfer voltage to be applied to the transfer roller 9 such that a current passing through the transfer roller 9 from the photosensitive drum 7 becomes a predetermined current.
- the controller 100 specifies, as a transfer current, a value corresponding to a difference between a surface potential (e.g., an exposure potential) of the photosensitive drum 7 that has undergone exposure and a developing voltage.
- the controller 100 specifies the transfer current as a necessary current for transferring a toner image onto a sheet S from the circumferential surface of the photosensitive drum 7 .
- the transfer voltage application circuit 32 is connected to the current sensor 32 A.
- the current sensor 32 A is configured to detect a transfer current passing through the transfer roller 9 .
- the current sensor 32 A is further configured to output, to the controller 100 , a detection signal corresponding to a transfer current passing through the transfer roller 9 when the transfer voltage application circuit 32 applies a transfer voltage to the transfer roller 9 .
- the developing roller 27 is electrically connected to a power supply (not illustrated).
- the developing roller 27 is configured to be applied with a predetermined voltage (e.g., a developing bias) based on a control signal such as a PWM signal outputted by the controller 100 during printing.
- the LED lamp 16 (an example of a charge eraser) is configured to irradiate the circumferential surface of the photosensitive drum 7 with light to erase charge from the surface of the photosensitive layer.
- the LED lamp 16 is connected to the controller 100 .
- the controller 100 controls the LED lamp 16 to turn on and off.
- the controller 100 is further configured to calculate a current I EX that may change in accordance with the quantity of accumulated charge to be cancelled out by charge generated inside the photosensitive layer by charging.
- the obtained current I EX may be useful for decreasing influence of the quantity of charge accumulated inside the photosensitive layer of the photosensitive drum 7 , thereby enabling accurate stabilization of the surface potential of the photosensitive drum 7 .
- FIG. 3 an explanation will be provided on how to calculate such a current I E x.
- the charge roller 8 In response to application of a predetermined charge voltage V CH1 to the charge roller 8 while some charge has been accumulated inside the photosensitive layer of the photosensitive drum 7 but substantially no charge is present on the circumferential surface of the photosensitive drum 7 , the charge roller 8 applies a charge quantity Q C0 that is the same as a target charge quantity Q 0 to a predetermined portion of the photosensitive drum 7 . A current thus passes through the charge roller 8 , and the current sensor 31 A detects a charge current I C0 corresponding to the charge quantity Q C0 .
- the applied charge quantity Q C0 may decrease due to the influence of some of the accumulated charge (e.g., a charge quantity Q E x) inside the photosensitive layer.
- the reason that the applied charge quantity Q C0 may decrease may be considered as follows.
- an electric field is generated in the photosensitive layer.
- the generation of the electric field causes some accumulated charge having a polarity opposite to the applied charge to move to an outer surface of the photosensitive layer, thereby causing such an accumulated charge and the charge applied to the photosensitive drum 7 to cancel out each other.
- the predetermined portion of the photosensitive drum 7 may thus have a surface potential corresponding to a charge quantity Q 1 that is smaller than the target charge quantity Q 0 .
- a charge quantity Q TR corresponding to the transfer voltage moves to the transfer roller 9 from the predetermined portion of the photosensitive drum 7 .
- the current sensor 32 A thus detects a transfer current I TR corresponding to the charge quantity Q TR .
- a charge voltage V CH1 is applied to the charge roller 8 .
- the charge roller 8 applies a charge quantity Q C1 to the predetermined portion of the photosensitive drum 7 .
- the charge quantity Q C1 may correspond to a difference between a target surface potential and an actual surface potential of the photosensitive drum 7 .
- the current sensor 31 A thus detects a charge current I C1 corresponding to the charge quantity Q C1 .
- Equation 1 may be held.
- the charge quantity Q C1 may be expressed by Equation 2.
- the charge quantity Q C0 may be obtained as a current I C0 using the current sensor 31 A.
- the charge quantity Q TR may be also obtained as a current I TR using the current sensor 32 A.
- the charge quantity Q EX and the charge quantity Q EL1 might not be obtained using the current sensors 31 A and 32 A.
- using Equation 1 might not accomplish obtainment of the charge quantity Q EX (e.g., the accumulated charge quantity) that may decrease the charge quantity Q C0 to be applied to the predetermined portion. Therefore, the current I EX corresponding to the charge quantity Q EX might not be obtained accurately.
- the charge quantity Q C1 may be obtained as a current I C1 using the current sensor 31 A.
- the charge quantity Q TR may be also obtained as a current I TR using the current sensor 32 A.
- the current I EX corresponding to the charge quantity Q EX may thus be obtained using Equation 3.
- the surface potential of the predetermined portion of the photosensitive drum 7 becomes substantially 0 (zero). If, therefore, charge is erased from the predetermined portion of the photosensitive drum 7 using the LED lamp 16 between the first charge current detection and the second charge current detection, the charge current detected in the second current detection (e.g., the charge current I C1 ) may be the same current (e.g., I C0 ) as the charge current detected in the first current detection (e.g., the charge current I C0 ). The current I EX thus might not be obtained accurately.
- the calculated current I EX is added to the current I C0 corresponding to the target charge quantity Q 0 , thereby enabling calculation of a current I C2 and a charge voltage V CH2 to be used for printing.
- the current Ice passes through the photosensitive drum 7 . That is, the charge roller 8 applies a charge quantity Q C2 corresponding to the current Ice to the photosensitive drum 7 .
- the charge quantity Q C2 decreases due to the influence of the charge quantity Q EX and the target charge quantity Q 0 thus remains on the circumferential surface of the photosensitive drum 7 . Consequently, the surface potential of the photosensitive drum 7 may be stabilized accurately.
- the portion of the circumferential surface of the photosensitive drum 7 where no charge remains is suitable for detection of the charge current I C0 .
- a portion may have a relatively small charge quantity that does not influence on the calculation of the current I E x.
- that portion may include a portion from which charge has been erased using the LED lamp 16 , and a portion which has been self-discharged due to expiration of a long term period from stopping of rotation of the photosensitive drum 7 .
- the charge current I C0 may be a current that is to be applied to the charge roller 8 by the charge voltage application circuit 31 . More specifically, in one example, the charge current I C0 may be applied to the charge roller 8 for charging the circumferential surface of the photosensitive drum 7 that has not been charged yet after a predetermined time period has elapsed since the photosensitive drum 7 and the charge roller 8 stopped their operations. In another example, the charge current I C0 may be applied to the charge roller 8 for charging the circumferential surface of the photosensitive drum 7 from which charge has been erased.
- the portion of the circumferential surface of the photosensitive drum 7 which may be suitable for detection of the charge current I C1 may be a portion that faces again the charge roller 8 after having undergone first charging but have not undergone any processing that may influence on the charge quantity of the circumferential surface of the photosensitive drum 7 other than transferring.
- the processing that may influence on the charge quantity of the circumferential surface of the photosensitive drum 7 other than transferring may include, for example, exposure by the scanner, developing for supplying toner T onto the circumferential surface of the photosensitive drum 7 from the developing roller 27 , and charge erasure using the LED lamp 16 .
- Transferring that may influence on the charge quantity of the circumferential surface of the photosensitive drum 7 may include application of a transfer voltage to the transfer roller 9 , i.e., movement of charge from the circumferential surface of the photosensitive drum 7 to the circumferential surface of the transfer roller 9 .
- the controller 100 obtains the charge current I C1 during a non-printing period (i.e., while printing is not executed).
- the non-printing period may refer to a period in which although the photosensitive drum 7 is rotating by the motor 17 and electric power is being supplied to the charge roller 8 and the transfer roller 9 , the scanner 10 does not execute exposure, the developing roller 27 does not supply toner T onto the circumferential surface of the photosensitive drum 7 , nor the LED lamp 16 is not turned on for erasing charge from the photosensitive drum 7 .
- the period in which the developing roller 27 does not supply toner T onto the circumferential surface of the photosensitive drum 7 may include a period in which a developing bias is not being applied to the developing roller 27 and a period in which a developing voltage lower than the charge voltage is being applied.
- the charge current I C1 may be a current that is to be applied to the charge roller 8 by the charge voltage application circuit 31 while electric power is applied to the transfer roller 9 by the transfer voltage application circuit 32 in the non-printing period. More specifically, for example, the charge current I C1 may be applied to the charge roller 8 when charging is executed again on the charged predetermined portion of the circumferential surface of the photosensitive drum 7 that has been charged by the charge roller 8 in response to the charged predetermined portion facing the charge roller 8 by a full turn of rotation of the photosensitive drum 7 .
- the transfer current I TR may be detected at an appropriate timing.
- the controller 100 executes a constant current control for controlling the transfer current I TR , a detected current and a predetermined current for the constant current control are substantially the same current. The controller 100 may thus obtain the predetermined current prestored in the ROM 20 as the transfer current I TR .
- the controller 100 turn the LED lamp 16 on for a first predetermined time period and obtain, as the charge current I C0 , a current detected between the timing when a charge-erased portion of the circumferential surface of the photosensitive layer arrives at the position where the charge-erased portion faces the charge roller 8 and the timing at which the first predetermined time period elapses. This may thus enable accurate estimation of the charge quantity Q C0 to be applied by the charge roller 8 to the portion having no charge remaining on the circumferential surface of the photosensitive drum 7 .
- the controller 100 further detects the charge current I C1 at the portion that has been charged and from which charge has not been erased, in the surface of photosensitive layer. Therefore, in one example, the controller 100 may obtain, as the charge current I C1 , a current detected in the non-printing period and after the portion charged by the charge roller 8 faces the charge roller 8 again by a full turn of rotation of the photosensitive drum 7 . In another example, the controller 100 may obtain, as the charge current I C1 , a current detected before the charge-erased portion arrives at the position where the charge-erased portion faces the charge roller 8 . In still another example, the controller 100 may obtain, as the charge current I C1 , a current detected in the non-printing period and after the first predetermined time period elapses since the charge-erased portion arrived at the position where the charge-erased portion faces.
- the controller 100 is further configured to execute initial target current I TA0 calculation, charge voltage V 0 application, transfer voltage application, charge current I CH acquisition, current I EX1 calculation, target current I TA1 calculation, first charge voltage V CH adjustment, and charge voltage V CH determination, as well as image forming for forming an image onto a sheet S.
- initial target current I TA0 calculation charge voltage V 0 application, transfer voltage application, charge current I CH acquisition, current I EX1 calculation, target current I TA1 calculation, first charge voltage V CH adjustment, and charge voltage V CH determination, as well as image forming for forming an image onto a sheet S.
- step S 41 the controller 100 obtains a drum count that indicates the number of rotations of the photosensitive drum 7 .
- the controller 100 obtains a current ambient condition by obtaining temperature from a temperature sensor (e.g., step S 42 ).
- step S 42 the controller 100 determines whether the drum count is greater than or equal to a predetermined value (e.g., step S 1 ). More specifically, the controller 100 determines, based on the determination result of the drum count, whether a thickness of the photosensitive layer has changed.
- step S 2 if the controller 100 determines that a difference between the temperature obtained in step S 42 in response to receiving the preceding print instruction and the temperature obtained in step S 42 in response to receiving the ongoing print instruction is greater than or equal to a predetermined value (e.g., 5° C.), the controller 100 determines that the current ambient condition is different from the preceding ambient condition (e.g., NO in step S 2 ).
- a predetermined value e.g., 5° C.
- the controller 100 determines, based on the temperature (an example of a second parameter), a target potential for the surface potential of the photosensitive drum 7 , i.e., a target surface potential Et (e.g., step S 3 ).
- the target surface potential Et may be predetermined by experiments or simulations.
- the target surface potential Et may be specified to be, for example, 700 V.
- the temperature may be detected by a temperature sensor for detecting ambient temperature around the photosensitive drum 7 .
- the drum count in response to the drum count reaching or exceeding the predetermined value (e.g., a threshold), the drum count may be reset to zero.
- the threshold e.g., the predetermined value
- the predetermined value may be changed to another value.
- the controller 100 calculates an initial target current I TA0 for a charge current I CH , based on the target surface potential Et and a first parameter that changes in response to the thickness change of the photosensitive layer (e.g., step S 5 ).
- the first parameter may be, for example, the total number of rotations of the photosensitive drum 7 .
- a higher charge current e.g., a larger charge quantity Q 0 ) needs to be applied to the photosensitive drum 7 as the thickness of the photosensitive layer becomes thinner.
- the relationship between the first parameter and the initial target current I TA0 may be predetermined by experiments or simulations.
- the processing executed in each of steps S 3 and S 5 corresponds to the initial target current I TA0 calculation. That is, in the initial target current I TA0 calculation, the controller 100 calculates the initial target current I TA0 for the charge current, based on the target surface potential Et and the first parameter.
- the controller 100 obtains an adjusted charge voltage V 0 (e.g., step S 6 ). More specifically, for example, the controller 100 obtains the adjusted charge voltage V 0 by adjusting the charge voltage V CH such that the charge current I CH detected by the current sensor 31 A becomes equal to the initial target current I TA0 .
- the charge voltage V 0 may be the charge voltage V CH1 , and corresponds to an initial charge voltage.
- step S 6 the controller 100 executes the current I EX1 calculation for calculating a current I EX1 (e.g., step S 7 ).
- step S 7 the controller 100 executes the same or similar calculation for obtaining the current I EX .
- the controller 100 executes the charge voltage application for applying the charge voltage V 0 corresponding to the initial target current I TA0 to the charge roller 8 (e.g., step S 71 ). The controller 100 continues the charge voltage application until the current I EX1 calculation ends.
- step S 71 the controller 100 determines whether the predetermined portion of the circumferential surface of the photosensitive drum 7 that has been charged in the charge voltage application has arrived at the position where the predetermined portion faces the transfer roller 9 (e.g., step S 72 ). More specifically, for example, in step S 72 , the controller 100 may determine whether an elapsed time from the start of the application of the charge voltage V 0 has reached a predetermined time duration.
- step S 72 the controller 100 determines that the predetermined portion of the circumferential surface of the photosensitive drum 7 has arrived at the position where the predetermined portion faces the transfer roller 9 (e.g., YES in step S 72 ).
- the controller 100 executes the transfer voltage application for applying, to the transfer roller 9 , a transfer voltage corresponding to the transfer current I TR (e.g., steps S 73 ).
- step S 73 the controller 100 determines whether the predetermined portion whose surface potential has changed in the transfer voltage application has arrived again at the position where the predetermined portion faces the charge roller 8 (e.g., step S 74 ).
- step S 74 similar to step S 72 , the controller 100 may determine, based on the elapsed time, whether charged the predetermined portion has arrived again at the position where the predetermined portion faces the charge roller 8 .
- step S 74 the controller 100 determines that the predetermined portion has arrived again at the position where the predetermined portion faces the charge roller 8 (e.g., YES in step S 74 ), the controller 100 executes the charge current acquisition for acquiring a charge current I CH detected based on a detection signal received from the current sensor 31 A (e.g., step S 75 ).
- the charge voltage application started in step S 71 is being continued when the charge current acquisition I CH is executed.
- step S 75 therefore, the charge roller 8 is being applied with the charge voltage V 0 corresponding to the initial target current I TA0 .
- step S 75 the controller 100 acquires a transfer current I TR detected based on a detection signal received from the current sensor 32 A (e.g., step S 76 ). Subsequent to step S 76 , the controller 100 obtains the current I EX1 corresponding to an accumulated charge quantity. More specifically, the controller 100 calculates a difference between the charge current I CH and the transfer current I TR (e.g., step S 77 ). For example, the controller 100 calculates the current I EX1 using Equation 3. Requirements for detecting the charge current I CH (e.g., the condition of the surface potential of the photosensitive drum 7 ) are the same as the requirements for detecting the charge current I C1 .
- Equation 3 Requirements for detecting the charge current I CH (e.g., the condition of the surface potential of the photosensitive drum 7 ) are the same as the requirements for detecting the charge current I C1 .
- the controller 100 executes the target current I TA1 calculation (e.g., step S 8 ).
- the controller 100 calculates a target current I TA1 by adding the current I EX1 to the initial target current I TA0 (e.g., step S 8 ).
- the initial target current I TA0 corresponds to the current I C0 (refer to FIG. 3 ).
- the target current I TA1 corresponds to the current I C2 (refer to FIG. 3 ).
- the controller 100 executes the first charge voltage V CH adjustment (e.g., step S 9 ).
- the controller 100 obtains an adjusted charge voltage V 1 by adjusting the charge voltage V CH such that the charge current I CH detected based on a detection signal received from the current sensor 31 A becomes equal to the initial target current I TA1 .
- the controller 100 executes the charge voltage V CH determination (e.g., step S 10 ).
- the controller 100 determines the charge voltage V 1 obtained by the adjustment in the first charge voltage V CH adjustment as the charge voltage V CH to be applied for forming an image onto a sheet S.
- the charge voltage V 1 corresponds to the charge voltage V CH2 .
- step S 10 the controller 100 executes the image forming using the charge voltage V 1 determined in step S 10 (e.g., step S 11 ) and then ends the processing of FIG. 4 . If, in step S 2 , the controller 100 determines that the current ambient condition is the same as the preceding ambient condition (e.g., YES in step S 2 ), the controller 100 executes the image forming without changing the charge voltage V CH to be applied (e.g., step S 11 ). That is, the controller 100 skips the processing of steps S 3 to S 10 .
- the first illustrative embodiment may therefore achieve the following effects.
- the current I EX1 corresponding to the accumulated charge quantity is obtained based on the detection signal outputted by the current sensor 31 A and the current sensor 32 A. Therefore, as compared with a known method for predicting an accumulated charge quantity, the control according to the first illustrative embodiment may more reduce an influence of the accumulated charge quantity on the applied charge voltage, thereby enabling accurate stabilization of the surface potential of the photosensitive drum 7 .
- a second illustrative embodiment will be described with reference to appropriate accompanying drawings.
- details of some of the operations and processing to be executed by the controller 100 may be different from those according to the first illustrative embodiment. Therefore, common components or steps have the same reference numerals or step numbers as those of the third illustrative embodiment, and the detailed description of the common components or steps is omitted.
- the controller 100 is further configured to execute test voltage application, charge current I CH acquisition, current I EX2 calculation, first determination, second determination, current I EXn calculation, target current correction, target current I TA2 calculation, second charge voltage V CH adjustment, as well as the various processing executed according to the first illustrative embodiment. Referring to FIG. 6 , an explanation will be provided on details of such various processing executed by the controller 100 .
- the controller 100 is further configured to execute processing of steps S 21 to S 30 in addition to the processing of steps of S 1 to S 11 according to the first illustrative embodiment.
- the controller 100 executes the test voltage application (e.g., step S 21 ).
- the controller 100 controls the charge voltage application circuit 31 to apply a test voltage Va to the charge roller 8 .
- the test voltage Va may be higher than the charge voltage V 0 corresponding to the initial target current I TA0 .
- the test voltage Va is applied to the charge roller 8 for obtaining a current I EX2 .
- the test voltage Va is not related to the target current I TAn for the charge current I CH .
- the test voltage Va to be applied is preferably as high as possible. For example, the maximum charge voltage V CH may be specified for the test voltage Va.
- the relationships between the charge voltage V and the current I EX may be significantly different depending on the accumulated charge quantity in the photosensitive layer.
- a dashed line indicates an example relationship between the charge voltage V and the current I EX in a case where the accumulated charge quantity is relatively low.
- a double-dotted-and-dashed line indicates another example relationship between the charge voltage V and the current I EX in a case where the accumulated charge quantity is larger than that indicated by the dashed line.
- the controller 100 executes the current I EX2 calculation for calculating a current I EX2 (e.g., step S 22 ).
- the current I EX2 calculation may be the same or similar to the current I EX1 calculation. More specifically, for example, in the current I EX2 calculation, the controller 100 executes the same or similar processing to the processing of each of steps S 72 to S 77 .
- the controller 100 executes the transfer voltage application when the predetermined portion of the circumferential surface of the photosensitive drum 7 that has been charged in the test voltage application passes the position where the predetermined portion faces the transfer roller 9 (e.g., steps S 72 and S 73 ).
- step S 73 the controller 100 executes the charge current I CH acquisition (e.g., steps S 74 and S 75 ).
- the controller 100 acquires a charge current I CH detected based on a detection signal received from the current sensor 31 A while the charge voltage application circuit 31 applies the test voltage Va to the charge roller 8 .
- the controller 100 obtains the current I EX2 . More specifically, for example, the controller 100 calculates a difference between the charge current I CH and the transfer current I TR that passes through the transfer roller 9 during the transfer voltage application (e.g., step S 77 ). That is, in step S 22 , the controller 100 obtains the current I EX2 by calculating a difference between the charge current I CH detected based on a detection signal received from the current sensor 31 A and the transfer current I TR detected based on a detection signal received from the current sensor 32 A while the test voltage Va is applied to the charge roller 8 . Requirements for detecting the charge current I CH (e.g., the condition of the surface potential of the photosensitive drum 7 ) are the same as the requirements for detecting the charge current I C1 .
- the controller 100 calculates a difference between the charge current I CH and the transfer current I TR that passes through the transfer roller 9 during the transfer voltage application (e.g., step S 77 ). That is, in step S 22 , the controller 100 obtains
- the controller 100 executes the first determination (e.g., step S 23 ).
- the controller 100 determines whether the current I EX2 is lower than or equal to a threshold TH 1 .
- a threshold TH 1 may be predetermined by experiments or simulations. In one example, the threshold TH 1 may be 5 ⁇ A.
- step S 9 when the controller 100 adjusts the charge current V CH , the amount of change in the current I EX is sufficiently small. That is, the current I EX has only little influence on the applied charge voltage. Thus, the controller 100 may execute the image forming properly with application of the voltage V 1 corresponding to the target current I TA1 .
- step S 23 the controller 100 determines that I EX2 >TH 1 (e.g., NO in step S 23 ), it is conceivable that the accumulated charge quantity in the photosensitive layer may be relatively high.
- the controller 100 executes the following steps to obtain a target current I TAn with consideration given to the influence of the current I EX on the applied charge voltage. More specifically, for example, the controller 100 executes the target current I TA1 calculation (e.g., step S 24 ) and the first charge voltage V CH adjustment (e.g., step S 25 ), which are the same or similar to steps S 8 and S 9 , respectively.
- step S 26 the controller 100 executes the second determination (e.g., step S 26 ).
- the controller 100 determines whether a difference (V n ⁇ V n ⁇ 1 ) between the present voltage V n and the last voltage V n ⁇ 1 is smaller than or equal to a threshold TH 2 (e.g., step S 26 ). If the controller 100 determines, in the second determination, that V n ⁇ V n ⁇ 1 ⁇ TH 2 (e.g., YES in step S 26 ), the controller 100 determines the present voltage V n as the charge voltage V CH (e.g., step S 27 ), and then executes the image forming (e.g., step S 11 ).
- the controller 100 determines, in the second determination, whether a difference between the charge voltage V 1 obtained by the adjustment in the first charge voltage V CH adjustment and the charge voltage V 0 corresponding to the initial charge voltage is smaller than or equal to the threshold TH 2 . If the controller 100 determines, in the second determination, that V n ⁇ V n ⁇ 1 ⁇ TH 2 (e.g., YES in step S 26 ), the controller 100 determines the charge voltage V 1 as the charge voltage V CH (e.g., step S 27 ), and then executes the image forming (e.g., step S 11 ). Determining the charge voltage V 1 as the charge voltage V CH in step S 27 corresponds to the charge voltage V CH determination.
- the controller 100 determines that V n ⁇ V n ⁇ 1 ⁇ TH 2 , i.e., if the controller 100 determines that the difference between the present voltage V n and the last voltage V n ⁇ 1 is relatively small, the amount of change in the current I EX is sufficiently small (refer to FIG. 7 ). That is, a difference between the current I EX passing in response to application of the charge voltage V CH corresponding to the last voltage V n ⁇ 1 to the charge roller 8 and the current I EX passing in response to application of the charge voltage V CH corresponding to the present voltage V n to the charge roller 8 is relatively small. The current I EX may thus have only little influence on the applied charge voltage, thereby enabling the image forming properly using the present voltage V n .
- the threshold TH 2 may be predetermined by experiments or simulations. In one example, the threshold TH 2 may be 5 V.
- the controller 100 determines, in the second determination, that V n ⁇ V n ⁇ 1 >TH 2 (e.g., NO in step S 26 )
- the controller 100 executes the current I EXn calculation (e.g., step S 28 ).
- the controller 100 calculates a current I EXn using the charge voltage V CH corresponding to the present value V n and a predetermined function. More specifically, in a case where this is the first time that the controller 100 has executed the second determination (e.g., step S 26 ) since receiving the ongoing print instruction, the controller 100 calculates the current I EXn using the charge voltage V 1 obtained by the adjustment in the first charge voltage V CH adjustment and the predetermined function.
- the predetermined function may be a linear approximation formula F, which may be obtained by the charge voltage V 0 , the test voltage Va, the current I EX1 , and the current I EX2 (refer to FIG. 7 ).
- the controller 100 calculates the current I EXn by substituting the present voltage V n for the linear approximation formula F.
- step S 28 the controller 100 calculates another target current I TAn by adding the current I EXn to the initial target current I TA0 (e.g., step S 29 ).
- the processing of steps S 28 and S 29 corresponds to the target current correction.
- the controller 100 calculates, based on the initial target current I TA0 and the current I EXn , a target current I TA2 for the charge current. Calculating such a target current I TA2 corresponds to the target current I TA2 calculation.
- step S 29 the controller 100 obtains an adjusted voltage V n+1 by adjusting the charge voltage V CH such that the charge current I CH detected based on a detection signal received from the current sensor 31 A becomes equal to the initial target current I TAn (e.g., step S 30 ).
- step S 30 the controller 100 obtains an adjusted voltage V 2 by adjusting the charge voltage V CH such that the charge current I CH detected based on a detection signal received from the current sensor 31 A becomes equal to the initial target current I TA2 . Adjusting the charge voltage V CH as such corresponds to the second charge voltage V CH adjustment.
- step S 30 the controller 100 returns to step S 26 to execute the second determination again.
- the controller 100 executes the second determination for the second time (or subsequent times)
- the controller 100 uses the voltage V n+1 obtained at step S 30 as the present value V n .
- the controller 100 determines whether a different between the charge voltage V 2 obtained by the adjustment in the second charge voltage V CH adjustment and the charge voltage V 1 obtained by the adjustment in the first charge voltage V CH adjustment is smaller than or equal to the threshold TH 2 .
- the controller 100 determines that V 2 ⁇ V 1 ⁇ TH 2 (e.g., YES in step S 26 ). If the controller 100 determines that V 2 ⁇ V 1 ⁇ TH 2 (e.g., YES in step S 26 ), the controller 100 determines the charge voltage V 2 obtained by the adjustment in the second charge voltage V CH adjustment as the charge voltage V CH used for the image forming.
- the second illustrative embodiment may therefore achieve the following effects.
- the current I EX2 passing in response to the application of the test voltage Va higher than the charge voltage V 0 to the charge roller 8 is lower than or equal to the threshold TH 1 , the current I EX may have only little influence on the applied charge voltage, thereby enabling the image forming appropriately using the voltage V 1 corresponding to the target current I TA1 .
- the current I EX2 passing in response to the application of the test voltage Va higher than the charge voltage V 0 to the charge roller 8 is not lower than or equal to the threshold TH 1 , the current I EX may have only little influence on the applied charge voltage, thereby enabling the image forming appropriately using the voltage V 1 corresponding to the target current I TA1 .
- the controller 100 executes the target current correction until V n ⁇ V n ⁇ 1 ⁇ TH 2 is held. Such a control may thus reduce the influence of the current EX on the applied charge voltage.
- the predetermined function may be the linear approximation formula F, which may be obtained by the charge voltage V 0 , the test voltage Va, the current I EX1 , and the current I EX2 . Using such a linear approximation formula F may thus implement the target current correction properly.
- the first parameter that changes in accordance with the change of the thickness of the photosensitive layer may be the total number of rotations of the photosensitive drum 7 .
- the first parameter may be the total number of printed sheets or the total number of dots in printed image data.
- the second parameter is not limited to the temperature.
- the second parameter may be any parameter related to ambient condition.
- the second parameter may be humidity or a combination of temperature and humidity.
- step S 2 if the controller 100 determines that a difference between the humidity obtained in step S 42 in response to receiving the preceding print instruction and the humidity obtained in step S 42 in response to receiving the ongoing print instruction is greater than a predetermined threshold (e.g., 20%), the controller 100 determines that the current ambient condition is different from the preceding ambient condition (e.g., NO in step S 2 ).
- a predetermined threshold e.g. 20%
- the controller 100 calculates the target current I TA1 for the charge current I CH .
- the controller 100 may calculate the target current I TA1 for the charge current I CH .
- the controller 100 determines, in the first determination, whether the current I EX2 is lower than or equal to the threshold TH 1 . Nevertheless, in other embodiments, for example, the controller 100 may determine, in the first determination, whether a difference between the current I EX2 and the current I EX1 is lower than or equal to a threshold TH 3 . In such a case, also, the controller 100 may determine whether I EX2 ⁇ TH 3 +I EX1 is held, which means that the controller 100 determines whether the current I EX2 is lower than or equal to the threshold TH 1 (e.g., TH 3 +I EX1 ).
- the threshold TH 1 e.g., TH 3 +I EX1
- the image forming apparatus is not limited to the monochrome laser printer 1 , but in other embodiments, for example, may be a color printer, a copying machine, and a multifunction device.
- the charger is not limited to the charge roller 8 , but in other embodiments, for example, may be a scorotron charger.
- the photosensitive member is not limited to the photosensitive drum 7 , but in other embodiments, for example, may be a belt-shaped member.
- the transfer medium is not limited to the sheet S, but in other embodiments, for example, may be an envelope or a film.
- the transfer member may be, for example, an intermediate transfer belt.
- the transfer member is not limited to the transfer roller 9 , but in other embodiments, for example, may be another member to which the transfer voltage may be applied, such as a conductive brush or a conductive leaf spring.
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Abstract
Description
- This application claims priority from Japanese Patent Application No. 2017-230450 filed on Nov. 30, 2017, the content of which is incorporated herein by reference in its entirety.
- Aspects disclosed herein relate to an image forming apparatus including a photosensitive member, a method of controlling the image forming apparatus, and a non-transitory computer-readable storage medium storing a program.
- Some known electrophotographic image forming apparatuses, for example, form a developer image onto a photosensitive layer of a photosensitive member. The photosensitive member contacts a member, and slides relative to the member during rotation. Sliding of the photosensitive member relative to the member causes friction therebetween, thereby causing charge accumulation inside the photosensitive layer of the photosensitive drum. Such charge accumulation may change a relationship between a charge current, which passes through a charger for charging the photosensitive member, and a surface potential of the photosensitive member, thereby failing to control the surface potential of the photosensitive drum to have a desired surface potential.
- In order to solve such a problem, some known technique has been used. In the known technique, for example, an accumulated charge quantity in the photosensitive layer is predicted. Based on the prediction, the larger the accumulated charge quantity is present, the greater the absolute value is specified for a charge voltage or the charge current (e.g., the magnitude of the charge voltage or charge current is increased over the magnitude of an initial charge voltage or charge current). More specifically, in the known technique, the accumulated charge quantity is predicted based on, for example, a transfer current, a rotating speed of the photosensitive member, and/or temperature.
- The following summary presents a simplified summary of certain features. The summary is not an extensive overview and is not intended to identify key or critical elements.
- Apparatus, methods, and computer-readable mediums are described for adjusting a charge voltage for a photosensitive member to account for accumulated charge quantity. In one example, currents related to charging a charger, which imparts a charge to a photosensitive member, are monitored. Based on the monitored currents, a new charging voltage may be determined and applied that accounts for accumulated charge quantity in the photosensitive member. A transfer current related to a transfer charge may also be monitored or a predetermined value used. The determination of the new charging voltage may be performed at various times.
- These and other features and advantages are described in greater detail below.
- Aspects of the disclosure are illustrated by way of example and not by limitation in the accompanying figures in which like reference characters indicate similar elements.
-
FIG. 1 is a sectional view illustrating an image forming apparatus in a first illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 2 illustrates an internal configuration of the image forming apparatus in the first illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 3 is a diagram for explaining how to calculate a charge quantity in a circumferential surface of a photosensitive drum in the first illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 4 is a flowchart of processing executed by a controller in the first illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 5 is a flowchart of current IEX1 calculation in the first illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 6 is a flowchart of processing executed by the controller in a second illustrative embodiment according to one or more aspects of the disclosure. -
FIG. 7 is a graph showing a relationship between a charge voltage, a current IEX, and an accumulated charge quantity in the second illustrative embodiment according to one or more aspects of the disclosure. - Hereinafter, an image forming apparatus according to a first illustrative embodiment will be described.
- The image forming apparatus may be a
laser printer 1. Thelaser printer 1 is configured to form an image onto a sheet S (an example of a transfer medium). Thelaser printer 1 includes acasing 2, afeed tray 3, amultipurpose tray 4, aprocess unit 5, a fixingunit 6, and acontroller 100. Thelaser printer 1 further includes adisplay 35. - The
process unit 5 is configured to form a developer image onto a sheet S. Theprocess unit 5 includes a photosensitive drum 7 (an example of a photosensitive member), a charge roller 8 (an example of a charger), a transfer roller 9 (an example of a transfer member), ascanner 10, and adeveloper cartridge 20. - The
scanner 10 is disposed in an upper portion of thecasing 2. Thescanner 10 includes a laser source (not illustrated), apolygon mirror 11,reflectors 12 and lenses (not illustrated). In thescanner 10, the laser source emits a laser beam. The emitted laser beam travels to a circumferential surface of thephotosensitive drum 7 while being reflected off thepolygon mirror 11 and the reflectors and passing through the lenses. Thus, the laser beam scans the circumferential surface of thephotosensitive drum 7 at a high scanning speed. - The
developer cartridge 20 includes ahousing 21, anagitator 25, a developingroller 27, asupply roller 28, and ablade 29 for regulating a thickness of a toner layer. Thehousing 21 is configured to store toner T (an example of developer) therein. - The
housing 21 supports theagitator 25, the developingroller 27, and thesupply roller 28 rotatably. - The
charge roller 27 faces thephotosensitive drum 7. Thesupply roller 28 supplies toner T from a developer chamber of thehousing 21 onto a circumferential surface of the developingroller 27. The developingroller 27 further supplies toner T onto the circumferential surface of thephotosensitive drum 7. - The
photosensitive drum 7 includes a cylindrical base, and a photosensitive layer formed on an outer circumferential surface of the cylindrical base. The cylindrical base may be made of, for example, metal. Thephotosensitive drum 7 is configured to rotate clockwise inFIG. 1 . The photosensitive layer may be positively chargeable. The photosensitive layer may include a single layer. The photosensitive layer may be applied with coating for protection and/or increase of durability. - The
charge roller 8 is disposed above thephotosensitive drum 7. Thecharge roller 8 is configured to rotate while being in contact with the circumferential surface, i.e., the photosensitive layer, of thephotosensitive drum 7. - The
transfer roller 9 faces thephotosensitive drum 7. Thetransfer roller 9 is disposed below thephotosensitive drum 7. - The
laser printer 1 further includes acleaning blade 15. Thecleaning blade 15 is disposed downstream from thetransfer roller 9 in a rotating direction of thephotosensitive drum 7. Thecleaning blade 15 has one end that is in contact with the circumferential surface, i.e., the photosensitive layer, of thephotosensitive drum 7. - The
laser printer 1 further includes anLED lamp 16. TheLED lamp 16 is disposed downstream from thecleaning blade 15 in the rotating direction of thephotosensitive drum 7. - The
photosensitive drum 7 may be positively charged by thecharge roller 8 during rotation. Thescanner 10 then exposes the circumferential surface of thephotosensitive drum 7 with a laser beam to form an electrostatic latent image thereon. Thereafter, the developingroller 27 supplies toner T onto the circumferential surface of thephotosensitive drum 7 to form a toner image on the circumferential surface of thephotosensitive drum 7. While a sheet S passes between thephotosensitive drum 7 and thetransfer roller 9, the toner image is transferred onto the sheet P from thephotosensitive drum 7 by application of a transfer bias to thetransfer roller 9. - The fixing
unit 6 is disposed downstream from theprocess unit 5 in a direction in which a sheet S is conveyed. The fixingunit 6 includes a fixingroller 6A and apressure roller 6B. Thepressure roller 6B presses the fixingroller 6A. The fixingroller 6A includes a cylindrical body and a heater in an internal space of the cylindrical body. The fixingunit 6 fixes the toner image onto the sheet S by heat applied by the heater while sandwiching the sheet S between the fixingroller 6A and thepressure roller 6B. - As illustrated in
FIG. 2 , thecontroller 100 is configured to execute various operation controls such as receipt of print data, sheet feeding from thefeed tray 3 or themultipurpose tray 4, operations of various units such as theprocess unit 5 and the fixingunit 6, in accordance with one or more preinstalled programs. In other words, the one or more programs enable thecontroller 100 to execute various processing as described below. - More specifically, the
controller 100 includes a single or a plurality of electric circuits such as aCPU 110, aROM 120, and aRAM 130. TheROM 120 stores programs for controlling units and members of thelaser printer 1 and various data such as various settings. TheRAM 130 is used by theCPU 110 as a work space for executing the programs and as a storage space for storing data temporarily. TheCPU 110 executes various calculations based on, for example, instructions outputted by an external device (not illustrated) such as a general-purpose computer, signals outputted by acurrent sensor 31A (an example of a first sensor) or by acurrent sensor 32A (an example of a second sensor), the one or more programs and/or data read from theROM 120. - The
controller 100 is configured to control the units and members of thelaser printer 1 by outputting control signals to those units and members based on calculation results of theCPU 110. Thecontroller 100 is further configured to output, to the external device (e.g., the computer), signals responsive to an operating status of thelaser printer 1. - The
controller 100 is configured to control operations of thephotosensitive drum 7, thecharge roller 8, thetransfer roller 9, the developingroller 27, theLED lamp 16, and thescanner 10. - The
laser printer 1 further includes amotor 17 and a plurality of gears (not illustrated). Themotor 17 is connected to thephotosensitive drum 7 via the plurality of gears. Themotor 17 is configured to drive thephotosensitive drum 7. Thecontroller 100 is configured to control motion of thephotosensitive drum 7 by outputting a control signal such as a pulse width modulation (“PWM”) signal to themotor 17. More specifically, for example, thecontroller 100 controls thephotosensitive drum 7 to start or stop rotating via themotor 17. - The
charge roller 8 is electrically connected to a chargevoltage application circuit 31. The chargevoltage application circuit 31 is further electrically connected to thecontroller 100. The chargevoltage application circuit 31 is configured to apply a charge voltage to thecharge roller 8. Thecontroller 100 is further configured to control the chargevoltage application circuit 31 by outputting a control signal such as a PWM signal to the chargevoltage application circuit 31. More specifically, for example, thecontroller 100 controls the chargevoltage application circuit 31 to supply electric power to thecharge roller 8. Thecontroller 100 specifies a charge voltage to be applied to thecharge roller 8 such that the surface potential of the circumferential surface of thephotosensitive drum 7 becomes a predetermined potential. The chargevoltage application circuit 31 is connected to thecurrent sensor 31A. Thecurrent sensor 31A is configured to detect a charge current passing through thecharge roller 8. Thecurrent sensor 31A is further configured to output, to thecontroller 100, a detection signal corresponding to a charge current passing through thecharge roller 8 when the chargevoltage application circuit 31 applies a charge voltage to thecharge roller 8. - The
transfer roller 9 is electrically connected to a transfervoltage application circuit 32. The transfervoltage application circuit 32 is further electrically connected to thecontroller 100. The transfervoltage application circuit 32 is configured to apply a transfer voltage to thetransfer roller 9. Thecontroller 100 is further configured to control the transfervoltage application circuit 32 by outputting a control signal such as a PWM signal to the transfervoltage application circuit 32. More specifically, for example, thecontroller 100 controls the transfervoltage application circuit 32 to supply electric power to thetransfer roller 9. Thecontroller 100 controls a transfer voltage to be applied to thetransfer roller 9 such that a current passing through thetransfer roller 9 from thephotosensitive drum 7 becomes a predetermined current. More specifically, for example, thecontroller 100 specifies, as a transfer current, a value corresponding to a difference between a surface potential (e.g., an exposure potential) of thephotosensitive drum 7 that has undergone exposure and a developing voltage. In other words, thecontroller 100 specifies the transfer current as a necessary current for transferring a toner image onto a sheet S from the circumferential surface of thephotosensitive drum 7. The transfervoltage application circuit 32 is connected to thecurrent sensor 32A. Thecurrent sensor 32A is configured to detect a transfer current passing through thetransfer roller 9. Thecurrent sensor 32A is further configured to output, to thecontroller 100, a detection signal corresponding to a transfer current passing through thetransfer roller 9 when the transfervoltage application circuit 32 applies a transfer voltage to thetransfer roller 9. - The developing
roller 27 is electrically connected to a power supply (not illustrated). The developingroller 27 is configured to be applied with a predetermined voltage (e.g., a developing bias) based on a control signal such as a PWM signal outputted by thecontroller 100 during printing. - The LED lamp 16 (an example of a charge eraser) is configured to irradiate the circumferential surface of the
photosensitive drum 7 with light to erase charge from the surface of the photosensitive layer. TheLED lamp 16 is connected to thecontroller 100. Thecontroller 100 controls theLED lamp 16 to turn on and off. - The
controller 100 is further configured to calculate a current IEX that may change in accordance with the quantity of accumulated charge to be cancelled out by charge generated inside the photosensitive layer by charging. The obtained current IEX may be useful for decreasing influence of the quantity of charge accumulated inside the photosensitive layer of thephotosensitive drum 7, thereby enabling accurate stabilization of the surface potential of thephotosensitive drum 7. Hereinafter, referring toFIG. 3 , an explanation will be provided on how to calculate such a current IEx. - In response to application of a predetermined charge voltage VCH1 to the
charge roller 8 while some charge has been accumulated inside the photosensitive layer of thephotosensitive drum 7 but substantially no charge is present on the circumferential surface of thephotosensitive drum 7, thecharge roller 8 applies a charge quantity QC0 that is the same as a target charge quantity Q0 to a predetermined portion of thephotosensitive drum 7. A current thus passes through thecharge roller 8, and thecurrent sensor 31A detects a charge current IC0 corresponding to the charge quantity QC0. - Nevertheless, in the
photosensitive drum 7, the applied charge quantity QC0 may decrease due to the influence of some of the accumulated charge (e.g., a charge quantity QEx) inside the photosensitive layer. The reason that the applied charge quantity QC0 may decrease may be considered as follows. In response to the application of the charge quantity QC0 to the circumferential surface of thephotosensitive drum 7, an electric field is generated in the photosensitive layer. The generation of the electric field causes some accumulated charge having a polarity opposite to the applied charge to move to an outer surface of the photosensitive layer, thereby causing such an accumulated charge and the charge applied to thephotosensitive drum 7 to cancel out each other. The predetermined portion of thephotosensitive drum 7 may thus have a surface potential corresponding to a charge quantity Q1 that is smaller than the target charge quantity Q0. - Thereafter, in response to application of a transfer voltage to the
transfer roller 9 when the predetermined portion of thephotosensitive drum 7 arrives at (e.g., faces) thetransfer roller 9, a charge quantity QTR corresponding to the transfer voltage moves to thetransfer roller 9 from the predetermined portion of thephotosensitive drum 7. Thecurrent sensor 32A thus detects a transfer current ITR corresponding to the charge quantity QTR. Until the predetermined portion of thephotosensitive drum 7 arrives at the position where the predetermined portion faces thetransfer roller 9 after passing a position where the predetermined portion faces thecharge roller 8, exposure by thescanner 10 and developing for supplying toner T by the developingroller 27 are not executed. - After that, when the predetermined portion of the
photosensitive drum 7 arrives again at the position where the predetermined portion faces thecharge roller 8 without any charge being erased therefrom using theLED lamp 16, a charge voltage VCH1 is applied to thecharge roller 8. In response, thecharge roller 8 applies a charge quantity QC1 to the predetermined portion of thephotosensitive drum 7. The charge quantity QC1 may correspond to a difference between a target surface potential and an actual surface potential of thephotosensitive drum 7. Thecurrent sensor 31A thus detects a charge current IC1 corresponding to the charge quantity QC1. - In a case where charge is erased from the predetermined portion of the
photosensitive drum 7 using theLED lamp 16, the surface potential of the predetermined portion of thephotosensitive drum 7 becomes substantially 0 (zero). Assuming that the charge quantity erased using theLED lamp 16 is QEL1,Equation 1 may be held. -
Q c0 =Q EX +Q TR +Q EL1 Equation 1 - In a case where charge is not erased from the predetermined portion of the
photosensitive drum 7 using theLED lamp 16, the charge quantity QC1 may be expressed byEquation 2. -
Q C1 =Q EX +Q TR Equation 2 - In
Equation 1, the charge quantity QC0 may be obtained as a current IC0 using thecurrent sensor 31A. The charge quantity QTR may be also obtained as a current ITR using thecurrent sensor 32A. Nevertheless, the charge quantity QEX and the charge quantity QEL1 might not be obtained using thecurrent sensors Equation 1 might not accomplish obtainment of the charge quantity QEX (e.g., the accumulated charge quantity) that may decrease the charge quantity QC0 to be applied to the predetermined portion. Therefore, the current IEX corresponding to the charge quantity QEX might not be obtained accurately. - In
Equation 2, the charge quantity QC1 may be obtained as a current IC1 using thecurrent sensor 31A. The charge quantity QTR may be also obtained as a current ITR using thecurrent sensor 32A. The current IEX corresponding to the charge quantity QEX may thus be obtained usingEquation 3. -
I EX =I C1 −I TREquation 3 - As described above, in a case where charge is erased from the predetermined portion of the
photosensitive drum 7 using theLED lamp 16, the surface potential of the predetermined portion of thephotosensitive drum 7 becomes substantially 0 (zero). If, therefore, charge is erased from the predetermined portion of thephotosensitive drum 7 using theLED lamp 16 between the first charge current detection and the second charge current detection, the charge current detected in the second current detection (e.g., the charge current IC1) may be the same current (e.g., IC0) as the charge current detected in the first current detection (e.g., the charge current IC0). The current IEX thus might not be obtained accurately. Nevertheless, in the illustrative embodiment, after a transfer voltage is applied to the predetermined portion of thephotosensitive drum 7, charging may be executed again on the predetermined portion without any charge having been erased therefrom. Such a control may thus enable calculation of the current IEX corresponding to the charge quantity QEX. Therefore, the current IEX may be calculated usingEquation 3. - The calculated current IEX is added to the current IC0 corresponding to the target charge quantity Q0, thereby enabling calculation of a current IC2 and a charge voltage VCH2 to be used for printing. In printing, in response to application of the charge voltage VCH2 to the predetermined portion of the
photosensitive drum 7, the current Ice passes through thephotosensitive drum 7. That is, thecharge roller 8 applies a charge quantity QC2 corresponding to the current Ice to thephotosensitive drum 7. In response, the charge quantity QC2 decreases due to the influence of the charge quantity QEX and the target charge quantity Q0 thus remains on the circumferential surface of thephotosensitive drum 7. Consequently, the surface potential of thephotosensitive drum 7 may be stabilized accurately. - The portion of the circumferential surface of the
photosensitive drum 7 where no charge remains is suitable for detection of the charge current IC0. Such a portion may have a relatively small charge quantity that does not influence on the calculation of the current IEx. For example, that portion may include a portion from which charge has been erased using theLED lamp 16, and a portion which has been self-discharged due to expiration of a long term period from stopping of rotation of thephotosensitive drum 7. - That is, the charge current IC0 may be a current that is to be applied to the
charge roller 8 by the chargevoltage application circuit 31. More specifically, in one example, the charge current IC0 may be applied to thecharge roller 8 for charging the circumferential surface of thephotosensitive drum 7 that has not been charged yet after a predetermined time period has elapsed since thephotosensitive drum 7 and thecharge roller 8 stopped their operations. In another example, the charge current IC0 may be applied to thecharge roller 8 for charging the circumferential surface of thephotosensitive drum 7 from which charge has been erased. - The portion of the circumferential surface of the
photosensitive drum 7 which may be suitable for detection of the charge current IC1 may be a portion that faces again thecharge roller 8 after having undergone first charging but have not undergone any processing that may influence on the charge quantity of the circumferential surface of thephotosensitive drum 7 other than transferring. The processing that may influence on the charge quantity of the circumferential surface of thephotosensitive drum 7 other than transferring may include, for example, exposure by the scanner, developing for supplying toner T onto the circumferential surface of thephotosensitive drum 7 from the developingroller 27, and charge erasure using theLED lamp 16. Transferring that may influence on the charge quantity of the circumferential surface of thephotosensitive drum 7 may include application of a transfer voltage to thetransfer roller 9, i.e., movement of charge from the circumferential surface of thephotosensitive drum 7 to the circumferential surface of thetransfer roller 9. In the illustrative embodiment, thecontroller 100 obtains the charge current IC1 during a non-printing period (i.e., while printing is not executed). In the illustrative embodiment, the non-printing period may refer to a period in which although thephotosensitive drum 7 is rotating by themotor 17 and electric power is being supplied to thecharge roller 8 and thetransfer roller 9, thescanner 10 does not execute exposure, the developingroller 27 does not supply toner T onto the circumferential surface of thephotosensitive drum 7, nor theLED lamp 16 is not turned on for erasing charge from thephotosensitive drum 7. The period in which the developingroller 27 does not supply toner T onto the circumferential surface of thephotosensitive drum 7 may include a period in which a developing bias is not being applied to the developingroller 27 and a period in which a developing voltage lower than the charge voltage is being applied. - That is, the charge current IC1 may be a current that is to be applied to the
charge roller 8 by the chargevoltage application circuit 31 while electric power is applied to thetransfer roller 9 by the transfervoltage application circuit 32 in the non-printing period. More specifically, for example, the charge current IC1 may be applied to thecharge roller 8 when charging is executed again on the charged predetermined portion of the circumferential surface of thephotosensitive drum 7 that has been charged by thecharge roller 8 in response to the charged predetermined portion facing thecharge roller 8 by a full turn of rotation of thephotosensitive drum 7. - In the illustrative embodiment, the transfer current ITR may be detected at an appropriate timing. In a case where the
controller 100 executes a constant current control for controlling the transfer current ITR, a detected current and a predetermined current for the constant current control are substantially the same current. Thecontroller 100 may thus obtain the predetermined current prestored in theROM 20 as the transfer current ITR. - In a case where the charge current IC0 is obtained while the
LED lamp 16 is on, it is preferable that thecontroller 100 turn theLED lamp 16 on for a first predetermined time period and obtain, as the charge current IC0, a current detected between the timing when a charge-erased portion of the circumferential surface of the photosensitive layer arrives at the position where the charge-erased portion faces thecharge roller 8 and the timing at which the first predetermined time period elapses. This may thus enable accurate estimation of the charge quantity QC0 to be applied by thecharge roller 8 to the portion having no charge remaining on the circumferential surface of thephotosensitive drum 7. - The
controller 100 further detects the charge current IC1 at the portion that has been charged and from which charge has not been erased, in the surface of photosensitive layer. Therefore, in one example, thecontroller 100 may obtain, as the charge current IC1, a current detected in the non-printing period and after the portion charged by thecharge roller 8 faces thecharge roller 8 again by a full turn of rotation of thephotosensitive drum 7. In another example, thecontroller 100 may obtain, as the charge current IC1, a current detected before the charge-erased portion arrives at the position where the charge-erased portion faces thecharge roller 8. In still another example, thecontroller 100 may obtain, as the charge current IC1, a current detected in the non-printing period and after the first predetermined time period elapses since the charge-erased portion arrived at the position where the charge-erased portion faces. - The
controller 100 is further configured to execute initial target current ITA0 calculation, charge voltage V0 application, transfer voltage application, charge current ICH acquisition, current IEX1 calculation, target current ITA1 calculation, first charge voltage VCH adjustment, and charge voltage VCH determination, as well as image forming for forming an image onto a sheet S. Referring toFIG. 4 , an explanation will be provided on control executed by thecontroller 100 and details of the various processing executed by thecontroller 100. - In response to receipt of a print instruction (e.g., START), the
controller 100 executes processing ofFIG. 4 . In step S41, thecontroller 100 obtains a drum count that indicates the number of rotations of thephotosensitive drum 7. Subsequent to step S41, thecontroller 100 obtains a current ambient condition by obtaining temperature from a temperature sensor (e.g., step S42). Subsequent to step S42, thecontroller 100 determines whether the drum count is greater than or equal to a predetermined value (e.g., step S1). More specifically, thecontroller 100 determines, based on the determination result of the drum count, whether a thickness of the photosensitive layer has changed. - If the
controller 100 determines that the drum count is not greater than or equal to the predetermined value (e.g., NO in step S1), thecontroller 100 determines whether the current ambient condition is the same as the ambient condition occurred at the time of receiving the preceding print instruction (e.g., step S2). More specifically, in step S2, if thecontroller 100 determines that a difference between the temperature obtained in step S42 in response to receiving the preceding print instruction and the temperature obtained in step S42 in response to receiving the ongoing print instruction is greater than or equal to a predetermined value (e.g., 5° C.), thecontroller 100 determines that the current ambient condition is different from the preceding ambient condition (e.g., NO in step S2). - If the
controller 100 determines that the current ambient condition is different from the preceding ambient condition (e.g., NO in step S2) or if thecontroller 100 determines that the drum count is greater than or equal to the predetermined value (e.g., YES in step S1), thecontroller 100 determines, based on the temperature (an example of a second parameter), a target potential for the surface potential of thephotosensitive drum 7, i.e., a target surface potential Et (e.g., step S3). The target surface potential Et may be predetermined by experiments or simulations. The target surface potential Et may be specified to be, for example, 700 V. The temperature may be detected by a temperature sensor for detecting ambient temperature around thephotosensitive drum 7. - In the illustrative embodiment, in response to the drum count reaching or exceeding the predetermined value (e.g., a threshold), the drum count may be reset to zero. Nevertheless, in other embodiments, for example, in response to the drum count reaching or exceeding the predetermined value, the threshold (e.g., the predetermined value) may be changed to another value.
- Subsequent to step S3, the
controller 100 calculates an initial target current ITA0 for a charge current ICH, based on the target surface potential Et and a first parameter that changes in response to the thickness change of the photosensitive layer (e.g., step S5). The first parameter may be, for example, the total number of rotations of thephotosensitive drum 7. As the photosensitive layer becomes thinner, static capacitance C increases. Therefore, for obtaining a constant target surface potential Et at the circumferential surface of thephotosensitive drum 7, a higher charge current (e.g., a larger charge quantity Q0) needs to be applied to thephotosensitive drum 7 as the thickness of the photosensitive layer becomes thinner. It may be considered, for example, that as the total number of rotations of thephotosensitive drum 7 increases, the photosensitive layer becomes thinner Thus, as the total number of rotations of thephotosensitive drum 7 increases, a greater target value may be specified for the charge current. The relationship between the first parameter and the initial target current ITA0 may be predetermined by experiments or simulations. - The processing executed in each of steps S3 and S5 corresponds to the initial target current ITA0 calculation. That is, in the initial target current ITA0 calculation, the
controller 100 calculates the initial target current ITA0 for the charge current, based on the target surface potential Et and the first parameter. - Subsequent to step S5, the
controller 100 obtains an adjusted charge voltage V0 (e.g., step S6). More specifically, for example, thecontroller 100 obtains the adjusted charge voltage V0 by adjusting the charge voltage VCH such that the charge current ICH detected by thecurrent sensor 31A becomes equal to the initial target current ITA0. The charge voltage V0 may be the charge voltage VCH1, and corresponds to an initial charge voltage. - Subsequent to step S6, the
controller 100 executes the current IEX1 calculation for calculating a current IEX1 (e.g., step S7). In step S7, thecontroller 100 executes the same or similar calculation for obtaining the current IEX. - More specifically, as illustrated in
FIG. 5 , in the current IEX1 calculation, after starting rotation of thephotosensitive drum 7, thecontroller 100 executes the charge voltage application for applying the charge voltage V0 corresponding to the initial target current ITA0 to the charge roller 8 (e.g., step S71). Thecontroller 100 continues the charge voltage application until the current IEX1 calculation ends. - Subsequent to step S71, the
controller 100 determines whether the predetermined portion of the circumferential surface of thephotosensitive drum 7 that has been charged in the charge voltage application has arrived at the position where the predetermined portion faces the transfer roller 9 (e.g., step S72). More specifically, for example, in step S72, thecontroller 100 may determine whether an elapsed time from the start of the application of the charge voltage V0 has reached a predetermined time duration. - If, in step S72, the
controller 100 determines that the predetermined portion of the circumferential surface of thephotosensitive drum 7 has arrived at the position where the predetermined portion faces the transfer roller 9 (e.g., YES in step S72), thecontroller 100 executes the transfer voltage application for applying, to thetransfer roller 9, a transfer voltage corresponding to the transfer current ITR (e.g., steps S73). Subsequent to step S73, thecontroller 100 determines whether the predetermined portion whose surface potential has changed in the transfer voltage application has arrived again at the position where the predetermined portion faces the charge roller 8 (e.g., step S74). In step S74, similar to step S72, thecontroller 100 may determine, based on the elapsed time, whether charged the predetermined portion has arrived again at the position where the predetermined portion faces thecharge roller 8. - If, in step S74, the
controller 100 determines that the predetermined portion has arrived again at the position where the predetermined portion faces the charge roller 8 (e.g., YES in step S74), thecontroller 100 executes the charge current acquisition for acquiring a charge current ICH detected based on a detection signal received from thecurrent sensor 31A (e.g., step S75). The charge voltage application started in step S71 is being continued when the charge current acquisition ICH is executed. In step S75, therefore, thecharge roller 8 is being applied with the charge voltage V0 corresponding to the initial target current ITA0. - Subsequent to step S75, the
controller 100 acquires a transfer current ITR detected based on a detection signal received from thecurrent sensor 32A (e.g., step S76). Subsequent to step S76, thecontroller 100 obtains the current IEX1 corresponding to an accumulated charge quantity. More specifically, thecontroller 100 calculates a difference between the charge current ICH and the transfer current ITR (e.g., step S77). For example, thecontroller 100 calculates the current IEX1 usingEquation 3. Requirements for detecting the charge current ICH (e.g., the condition of the surface potential of the photosensitive drum 7) are the same as the requirements for detecting the charge current IC1. - Referring to
FIG. 4 , subsequent to step S7, thecontroller 100 executes the target current ITA1 calculation (e.g., step S8). In the target current ITA1 calculation, thecontroller 100 calculates a target current ITA1 by adding the current IEX1 to the initial target current ITA0 (e.g., step S8). The initial target current ITA0 corresponds to the current IC0 (refer toFIG. 3 ). The target current ITA1 corresponds to the current IC2 (refer toFIG. 3 ). - Subsequent to step S8, the
controller 100 executes the first charge voltage VCH adjustment (e.g., step S9). In the first charge voltage VCH adjustment, thecontroller 100 obtains an adjusted charge voltage V1 by adjusting the charge voltage VCH such that the charge current ICH detected based on a detection signal received from thecurrent sensor 31A becomes equal to the initial target current ITA1. Subsequent to step S9, thecontroller 100 executes the charge voltage VCH determination (e.g., step S10). In the charge voltage VCH determination, thecontroller 100 determines the charge voltage V1 obtained by the adjustment in the first charge voltage VCH adjustment as the charge voltage VCH to be applied for forming an image onto a sheet S. The charge voltage V1 corresponds to the charge voltage VCH2. - Subsequent to step S10, the
controller 100 executes the image forming using the charge voltage V1 determined in step S10 (e.g., step S11) and then ends the processing ofFIG. 4 . If, in step S2, thecontroller 100 determines that the current ambient condition is the same as the preceding ambient condition (e.g., YES in step S2), thecontroller 100 executes the image forming without changing the charge voltage VCH to be applied (e.g., step S11). That is, thecontroller 100 skips the processing of steps S3 to S10. - The first illustrative embodiment may therefore achieve the following effects.
- The current IEX1 corresponding to the accumulated charge quantity is obtained based on the detection signal outputted by the
current sensor 31A and thecurrent sensor 32A. Therefore, as compared with a known method for predicting an accumulated charge quantity, the control according to the first illustrative embodiment may more reduce an influence of the accumulated charge quantity on the applied charge voltage, thereby enabling accurate stabilization of the surface potential of thephotosensitive drum 7. - A second illustrative embodiment will be described with reference to appropriate accompanying drawings. In the second illustrative embodiment, details of some of the operations and processing to be executed by the
controller 100 may be different from those according to the first illustrative embodiment. Therefore, common components or steps have the same reference numerals or step numbers as those of the third illustrative embodiment, and the detailed description of the common components or steps is omitted. - The
controller 100 is further configured to execute test voltage application, charge current ICH acquisition, current IEX2 calculation, first determination, second determination, current IEXn calculation, target current correction, target current ITA2 calculation, second charge voltage VCH adjustment, as well as the various processing executed according to the first illustrative embodiment. Referring toFIG. 6 , an explanation will be provided on details of such various processing executed by thecontroller 100. Thecontroller 100 is further configured to execute processing of steps S21 to S30 in addition to the processing of steps of S1 to S11 according to the first illustrative embodiment. - As illustrated in
FIG. 6 , subsequent to step S7, thecontroller 100 executes the test voltage application (e.g., step S21). In the test voltage application, thecontroller 100 controls the chargevoltage application circuit 31 to apply a test voltage Va to thecharge roller 8. The test voltage Va may be higher than the charge voltage V0 corresponding to the initial target current ITA0. The test voltage Va is applied to thecharge roller 8 for obtaining a current IEX2. The test voltage Va is not related to the target current ITAn for the charge current ICH. The test voltage Va to be applied is preferably as high as possible. For example, the maximum charge voltage VCH may be specified for the test voltage Va. - As illustrated in
FIG. 7 , the relationships between the charge voltage V and the current IEX may be significantly different depending on the accumulated charge quantity in the photosensitive layer. InFIG. 7 , a dashed line indicates an example relationship between the charge voltage V and the current IEX in a case where the accumulated charge quantity is relatively low. A double-dotted-and-dashed line indicates another example relationship between the charge voltage V and the current IEX in a case where the accumulated charge quantity is larger than that indicated by the dashed line. - As shown in the graph, in the case where the accumulated charge quantity is relatively low (e.g., the case indicated by the dashed line), an amount of change in the current IEX relative to an amount of change in the charge voltage V is relatively small. The greater the accumulated charge quantity, the greater the amount of change in the current IEX relative to the amount of change in the charge voltage V.
- As illustrated in
FIG. 6 , subsequent to step S21, thecontroller 100 executes the current IEX2 calculation for calculating a current IEX2 (e.g., step S22). The current IEX2 calculation may be the same or similar to the current IEX1 calculation. More specifically, for example, in the current IEX2 calculation, thecontroller 100 executes the same or similar processing to the processing of each of steps S72 to S77. In the current IEX2 calculation, thecontroller 100 executes the transfer voltage application when the predetermined portion of the circumferential surface of thephotosensitive drum 7 that has been charged in the test voltage application passes the position where the predetermined portion faces the transfer roller 9 (e.g., steps S72 and S73). - Subsequent to step S73, the
controller 100 executes the charge current ICH acquisition (e.g., steps S74 and S75). In the charge current ICH acquisition, when the predetermined portion whose surface potential has changed by the transfer voltage application passes again the position where the predetermined portion faces thecharge roller 8, thecontroller 100 acquires a charge current ICH detected based on a detection signal received from thecurrent sensor 31A while the chargevoltage application circuit 31 applies the test voltage Va to thecharge roller 8. - Subsequent to step S75, the
controller 100 obtains the current IEX2. More specifically, for example, thecontroller 100 calculates a difference between the charge current ICH and the transfer current ITR that passes through thetransfer roller 9 during the transfer voltage application (e.g., step S77). That is, in step S22, thecontroller 100 obtains the current IEX2 by calculating a difference between the charge current ICH detected based on a detection signal received from thecurrent sensor 31A and the transfer current ITR detected based on a detection signal received from thecurrent sensor 32A while the test voltage Va is applied to thecharge roller 8. Requirements for detecting the charge current ICH (e.g., the condition of the surface potential of the photosensitive drum 7) are the same as the requirements for detecting the charge current IC1. - Subsequent to step S22, the
controller 100 executes the first determination (e.g., step S23). In the first determination, thecontroller 100 determines whether the current IEX2 is lower than or equal to a threshold TH1. Such first determination may accomplish determination as to whether the accumulated charge quantity in the photosensitive layer is relatively small, as illustrated inFIG. 7 . The threshold TH1 may be predetermined by experiments or simulations. In one example, the threshold TH1 may be 5 μA. - As illustrated in
FIG. 6 , if thecontroller 100 determines, in the first determination, that IEX2≤TH1 (e.g., YES in step S23), thecontroller 100 executes the processing of each of steps S8 to S10. Subsequent to step S10, thecontroller 100 executes the image forming (e.g., step S11) and ends this control. Where IEX2≤TH1, it is conceivable that the accumulated charge quantity in the photosensitive layer may be relatively low. Thus, in step S9, when thecontroller 100 adjusts the charge current VCH, the amount of change in the current IEX is sufficiently small. That is, the current IEX has only little influence on the applied charge voltage. Thus, thecontroller 100 may execute the image forming properly with application of the voltage V1 corresponding to the target current ITA1. - If, in step S23, the
controller 100 determines that IEX2>TH1 (e.g., NO in step S23), it is conceivable that the accumulated charge quantity in the photosensitive layer may be relatively high. Thus, thecontroller 100 executes the following steps to obtain a target current ITAn with consideration given to the influence of the current IEX on the applied charge voltage. More specifically, for example, thecontroller 100 executes the target current ITA1 calculation (e.g., step S24) and the first charge voltage VCH adjustment (e.g., step S25), which are the same or similar to steps S8 and S9, respectively. - Subsequent to step S25, the
controller 100 executes the second determination (e.g., step S26). In the second determination, thecontroller 100 determines whether a difference (Vn−Vn−1) between the present voltage Vn and the last voltage Vn−1 is smaller than or equal to a threshold TH2 (e.g., step S26). If thecontroller 100 determines, in the second determination, that Vn−Vn−1≤TH2 (e.g., YES in step S26), thecontroller 100 determines the present voltage Vn as the charge voltage VCH (e.g., step S27), and then executes the image forming (e.g., step S11). - More specifically, for example, in a case where this is the first time that the
controller 100 has executed the second determination since receiving the ongoing print instruction, thecontroller 100 determines, in the second determination, whether a difference between the charge voltage V1 obtained by the adjustment in the first charge voltage VCH adjustment and the charge voltage V0 corresponding to the initial charge voltage is smaller than or equal to the threshold TH2. If thecontroller 100 determines, in the second determination, that Vn−Vn−1≤TH2 (e.g., YES in step S26), thecontroller 100 determines the charge voltage V1 as the charge voltage VCH (e.g., step S27), and then executes the image forming (e.g., step S11). Determining the charge voltage V1 as the charge voltage VCH in step S27 corresponds to the charge voltage VCH determination. - If the
controller 100 determines that Vn−Vn−1≤TH2, i.e., if thecontroller 100 determines that the difference between the present voltage Vn and the last voltage Vn−1 is relatively small, the amount of change in the current IEX is sufficiently small (refer toFIG. 7 ). That is, a difference between the current IEX passing in response to application of the charge voltage VCH corresponding to the last voltage Vn−1 to thecharge roller 8 and the current IEX passing in response to application of the charge voltage VCH corresponding to the present voltage Vn to thecharge roller 8 is relatively small. The current IEX may thus have only little influence on the applied charge voltage, thereby enabling the image forming properly using the present voltage Vn. The threshold TH2 may be predetermined by experiments or simulations. In one example, the threshold TH2 may be 5 V. - If the
controller 100 determines, in the second determination, that Vn−Vn−1>TH2 (e.g., NO in step S26), thecontroller 100 executes the current IEXn calculation (e.g., step S28). In the current IEXn calculation, thecontroller 100 calculates a current IEXn using the charge voltage VCH corresponding to the present value Vn and a predetermined function. More specifically, in a case where this is the first time that thecontroller 100 has executed the second determination (e.g., step S26) since receiving the ongoing print instruction, thecontroller 100 calculates the current IEXn using the charge voltage V1 obtained by the adjustment in the first charge voltage VCH adjustment and the predetermined function. More specifically, for example, the predetermined function may be a linear approximation formula F, which may be obtained by the charge voltage V0, the test voltage Va, the current IEX1, and the current IEX2 (refer toFIG. 7 ). Thecontroller 100 calculates the current IEXn by substituting the present voltage Vn for the linear approximation formula F. - Subsequent to step S28, the
controller 100 calculates another target current ITAn by adding the current IEXn to the initial target current ITA0 (e.g., step S29). The processing of steps S28 and S29 corresponds to the target current correction. In a case where this is the first time that thecontroller 100 has executed the target current correction since receiving the ongoing print instruction, thecontroller 100 calculates, based on the initial target current ITA0 and the current IEXn, a target current ITA2 for the charge current. Calculating such a target current ITA2 corresponds to the target current ITA2 calculation. - Subsequent to step S29, i.e., subsequent to the execution of the target current correction, the
controller 100 obtains an adjusted voltage Vn+1 by adjusting the charge voltage VCH such that the charge current ICH detected based on a detection signal received from thecurrent sensor 31A becomes equal to the initial target current ITAn (e.g., step S30). In a case where this is the first time that thecontroller 100 has executed the processing of step S30 since receiving the ongoing print instruction, in step S30, thecontroller 100 obtains an adjusted voltage V2 by adjusting the charge voltage VCH such that the charge current ICH detected based on a detection signal received from thecurrent sensor 31A becomes equal to the initial target current ITA2. Adjusting the charge voltage VCH as such corresponds to the second charge voltage VCH adjustment. - Subsequent to step S30, the
controller 100 returns to step S26 to execute the second determination again. When thecontroller 100 executes the second determination for the second time (or subsequent times), thecontroller 100 uses the voltage Vn+1 obtained at step S30 as the present value Vn. In the second determination for the second time, thecontroller 100 determines whether a different between the charge voltage V2 obtained by the adjustment in the second charge voltage VCH adjustment and the charge voltage V1 obtained by the adjustment in the first charge voltage VCH adjustment is smaller than or equal to the threshold TH2. If thecontroller 100 determines that V2−V1≤TH2 (e.g., YES in step S26), thecontroller 100 determines the charge voltage V2 obtained by the adjustment in the second charge voltage VCH adjustment as the charge voltage VCH used for the image forming. - The second illustrative embodiment may therefore achieve the following effects.
- In a case where the current IEX2 passing in response to the application of the test voltage Va higher than the charge voltage V0 to the
charge roller 8 is lower than or equal to the threshold TH1, the current IEX may have only little influence on the applied charge voltage, thereby enabling the image forming appropriately using the voltage V1 corresponding to the target current ITA1. - In a case where V1−V0≤TH2 although the current IEX2 passing in response to the application of the test voltage Va higher than the charge voltage V0 to the
charge roller 8 is not lower than or equal to the threshold TH1, the current IEX may have only little influence on the applied charge voltage, thereby enabling the image forming appropriately using the voltage V1 corresponding to the target current ITA1. - In a case where Vn−Vn−1>TH2, the
controller 100 executes the target current correction until Vn−Vn−1≤TH2 is held. Such a control may thus reduce the influence of the current EX on the applied charge voltage. - The predetermined function may be the linear approximation formula F, which may be obtained by the charge voltage V0, the test voltage Va, the current IEX1, and the current IEX2. Using such a linear approximation formula F may thus implement the target current correction properly.
- While the disclosure has been described in detail with reference to the specific embodiments thereof, these are merely examples, and various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure.
- In the illustrative embodiments, the first parameter that changes in accordance with the change of the thickness of the photosensitive layer may be the total number of rotations of the
photosensitive drum 7. Nevertheless, in other embodiments, for example, the first parameter may be the total number of printed sheets or the total number of dots in printed image data. The second parameter is not limited to the temperature. In other embodiments, for example, the second parameter may be any parameter related to ambient condition. For example, the second parameter may be humidity or a combination of temperature and humidity. For example, in a case where the second parameter is humidity, in step S2, if thecontroller 100 determines that a difference between the humidity obtained in step S42 in response to receiving the preceding print instruction and the humidity obtained in step S42 in response to receiving the ongoing print instruction is greater than a predetermined threshold (e.g., 20%), thecontroller 100 determines that the current ambient condition is different from the preceding ambient condition (e.g., NO in step S2). - In the illustrative embodiments, on condition that the
controller 100 determines that a new print instruction has been received and the drum count is greater than or equal to the predetermined value, thecontroller 100 calculates the target current ITA1 for the charge current ICH. Nevertheless, in other embodiments, for example, on condition that thecontroller 100 determines that power of the image forming apparatus is turned on and the drum count is greater than or equal to the predetermined value, thecontroller 100 may calculate the target current ITA1 for the charge current ICH. - In the second illustrative embodiment, the
controller 100 determines, in the first determination, whether the current IEX2 is lower than or equal to the threshold TH1. Nevertheless, in other embodiments, for example, thecontroller 100 may determine, in the first determination, whether a difference between the current IEX2 and the current IEX1 is lower than or equal to a threshold TH3. In such a case, also, thecontroller 100 may determine whether IEX2≤TH3+IEX1 is held, which means that thecontroller 100 determines whether the current IEX2 is lower than or equal to the threshold TH1 (e.g., TH3+IEX1). - The image forming apparatus is not limited to the
monochrome laser printer 1, but in other embodiments, for example, may be a color printer, a copying machine, and a multifunction device. - The charger is not limited to the
charge roller 8, but in other embodiments, for example, may be a scorotron charger. - The photosensitive member is not limited to the
photosensitive drum 7, but in other embodiments, for example, may be a belt-shaped member. - The transfer medium is not limited to the sheet S, but in other embodiments, for example, may be an envelope or a film. For an intermediate transfer laser printer, the transfer member may be, for example, an intermediate transfer belt.
- The transfer member is not limited to the
transfer roller 9, but in other embodiments, for example, may be another member to which the transfer voltage may be applied, such as a conductive brush or a conductive leaf spring. - The one or more aspects of the disclosure may be implemented in various combinations of the elements described in the illustrative embodiments and variations.
Claims (18)
I C0 +I C1 −I TR.
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2018
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Publication number | Priority date | Publication date | Assignee | Title |
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US10859939B2 (en) * | 2019-04-09 | 2020-12-08 | Fuji Xerox Co., Ltd. | Image forming apparatus |
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US10444657B2 (en) | 2019-10-15 |
JP6844517B2 (en) | 2021-03-17 |
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